This invention relates, in general, to motion detector circuits, and more particularly to high sensitivity motion detector circuits.
There are many types of electro-mechanical devices which manipulate small moving substances. Substance parameters such as speed, location, or substance size is common information needed by control circuitry. Obtaining this information accurately can be extremely difficult for substances of small sizes, substances traveling at high speeds, or for transmissive substances. Under these types of conditions, sensing circuitry must be able to detect very small signal levels generated by the substance. The difficulty with detecting small signal levels is that the magnitude of the signals may be very dose to noise levels of the system.
An example which embodies all conditions listed above is an ink jet printer. A small droplet is fired from a nozzle of an ink jet pen. The size of a droplet is approximately 70 picoliters and moves at a velocity exceeding 10 meters per second. Further adding to the problem is that an ink droplet is approximately 98% transmissive to infrared light which makes detection very difficult. A secondary problem is that ink jet printers also have multiple pens each firing a different color. A detection circuit must be able to equally detect characteristics of different colored ink droplets.
Generally, detection of a small moving substance, such as an ink droplet, involves a transmitted signal which the ink droplet disrupts and a receiver which detects changes in the transmitted signal. The receiver or sensor typically outputs a small signal which is amplified to increase signal magnitude. Sensing a substance becomes difficult when the substance is small or moves too fast to generate an appreciable signal. If the change in signal magnitude caused by the moving substance approaches noise levels at the input of the amplifier detection will be difficult.
Detection circuits currently being used are capable of sensing ink droplet sizes in the 70 picoliter range. Smaller droplet sizes (less than 70 picoliters) would generate signal levels which would be difficult to detect due to noise problems. Yet, smaller ink droplet sizes are being considered because printer resolution or print quality is directly related to ink droplet size. High resolution ink jet printers are being developed which fire ink droplets that are approximately 20 to 30 picoliters. It would be of great benefit if a circuit could be developed with increased sensitivity to allow detection of even smaller moving substances.